1. Field of the Invention
The present invention is directed to a rotating anode x-ray tube having a magnetic bearing arrangement used during operation of the tube, and a mechanical bearing arrangement for supporting the anode shaft in the event of the anode "dropping" and a magnetically actuatable contact for making and breaking a circuit to provide high voltage to the anode.
2. Description of the Prior Art
A rotating anode x-ray tube is disclosed in U.S. Pat. No. 4,167,671 having a cathode and the rotating anode contained in an evacuated housing, the rotating anode having a drive shaft which is magnetically seated within the housing during normal operation of the x-ray tube. The housing is also provided with mechanical bearings which support the shaft of the anode in the event of an anode "drop" or when the magnetic bearing arrangement is shut off when the tube is not in use. This known x-ray tube also has a magnetically actuatable anode contact for making and breaking the circuit which provides high voltage to the anode.
Mechanical bearings which are used for supporting the shaft of the rotating anode in x-ray tubes of this type must necessarily exhibit a certain play or slack to compensate for thermal expansion of the components during operation. The mechanical bearings in x-ray tubes of the type described above, which are used as a back-up in the event of failure or shut down of the magnetic bearing arrangement, intentionally are spaced from the anode shaft, so as not to interfere with the rotation of the drive shaft during normal operation, during which time the shaft is supported by the magnetic bearing arrangement. Such mechanical bearings only intercept the rotating system when the magnetic support ceases, i.e., when the anode "drops." When the x-ray tube of the type is shut down, therefore, the play in the bearings is considerable and, particularly during transport of a rotating anode x-ray tube of this type, the rotating anode is not rigidly held, but can move about inside the housing, possibly damaging the anode or other components.
As noted above, the voltage supply in the vacuum tube described in U.S. Pat. No. 4,167,671 is through a magnetically actuatable anode contact which connects the anode to one pole of a high voltage supply. This anode contact includes a male member which is guided in a bore disposed inside the evacuated housing. A slip contact is made between the surfaces of the male member and the bore, however, because the bore is located inside the evacuated housing, the surfaces cannot be lubricated, otherwise the vacuum would be contaminated.
A rotating anode x-ray tube is disclosed in European Application No. 0 154 699, corresponding to U.S. Pat. No. 4,628,522, having a magnetic bearing arrangement wherein the mechanical intercept bearings are rigidly connected to the housing, and the shaft has a pair of rings thereon. The rings engage the ball race of the bearing when the rotating anode drops. Again, however, this known mechanical bearing has a certain amount of play, so that the rotating anode in this device also knocks against the other components when the magnetic bearing is off.